1. Field of the Invention
The present invention relates to an image processing apparatus and an image processing method used for a scanner, a digital copying machine, and the like that read image information by scanning an original document with a CCD line sensor.
2. Description of the Related Art
As typical examples of a CCD line sensor used in a reducing optical system, there are a line sensor comprising a 1-line line sensor, and a sensor comprising a 3-line line sensor formed of three line sensors on the surfaces of which are respectively disposed color filters in red (hereinafter, occasionally abbreviated to R), green (hereinafter, occasionally abbreviated to G), and blue (hereinafter, occasionally abbreviated to B).
The 3-line CCD line sensor is basically used to read a color original document. In this case, a light source having oscillation wavelengths of 400 nm to 700 nm and thereby having spectral characteristics that sufficiently cover a visible light region is used, and separation of color information of R, G, and B is performed using the color filters disposed on the surfaces of the respective line sensors.
In addition, in a case where a monochrome original document is read using the 3-line CCD line sensor, there are a method by which one output from the 3-line CCD line sensor, that is, an output of the CCD line sensor for G in general, is used with the purpose of reading a seal in vermillion in a reliable manner, and a method by which black and white information is generated using all the outputs of the 3-line CCD line sensor.
According to these methods, whether an input original document is a color original document or a monochrome original document is determined using the 3-line line sensor comprising three line sensors on the surfaces of which are respectively disposed color filters, for example, in red, green and blue, and a color output is performed for a color original document and a monochrome output is performed for a monochrome original document at the time of output to the printer.
However, for an original document whose background alone is made of colors, a color output is performed because of the presence of a large number of color pixels regardless of the fact that they are not useful information as colors, which results in unnecessary consumption of toner particles.
Meanwhile, in a case where a monochrome output is performed for such an original document, the monochrome information can be calculated as:(red information+blue information+green information)/3.However, when this processing is used, for example, in a case where information is made of black characters on the base in blue, given that the outputs of the respective line sensors when reading the blue information of the base are (red:blue:green)=(40:60:120), and the outputs of the respective line sensors when reading the black character information are (red:blue:green)=(40:40:40), then,
(40+60+120)/3=73 when the blue base information is converted to monochrome, and
(40+40+40)/3=40 when the black character information is converted to monochrome.
It is therefore understood that when such a color original document is copied in monochrome, the densities are almost the same. Hence, in the case of the related art where whether an original document is a color original document or a monochrome original document is determined and an output is performed using the two methods, toner particles are consumed unnecessarily and smearing or fading occurs in the case of a monochrome output.
Similar techniques are disclosed in Official Gazette (A) JP-A-2003-274115 and Official Gazette (B) JP-A-11-187266. Official Gazette (A) describes a reading device using a 4-line line sensor but is silent about a correction of a monochrome signal using a color signal. Official Gazette (B) discloses a base removing method. However, it is configured so as to perform a density correction for RGB signals, and is different from the technique of the invention.